There is a well documented link between substance use problems and criminal activity in adolescence, with co-occurring involvement increasing risk for continued crime, substance use problems in adulthood, and poor treatment outcomes. To date, research on this link has focused mainly on etiology, mapping common and distinct pathways to the onset and maintenance of these problems. Longitudinal studies of substance use and delinquency in isolation, however, have shown that a large proportion of individuals with significant substance use problems or criminal involvement greatly reduce or stop these behaviors in their mid-20's (they "desist"). Very little is known about the processes behind this desistance (for either type of behavior or both behaviors conjointly). This study proposes to follow a group of serious adolescent offenders (N=1,355), already enrolled in an ongoing longitudinal investigation, into early adulthood to map out the process of desistance from substance use problems and crime. Comprehensive annual interviews will be conducted with these adolescents to document their criminal activities and substance use, psychosocial development, changes in social contexts (e.g., employment), and involvements with the legal system (e.g., institutional placements). Official records of legal system involvement will also be collected. Trajectory models will be used to describe the patterns of desistance of substance use problems and criminal involvement (both singly and conjointly). The impact of changes in psychosocial development, social contexts, and legal system involvement will be assessed on these processes, across the whole sample and within identified trajectory subgroups. These effects will also be examined in relationship to age, ethnicity, gender, substance use disorder, and criminal history. This study focuses a multidisciplinary, successful longitudinal investigation on the link between substance use and criminal involvement. The range of topics covered and the characteristics of the sample allow for an examination of how normative processes of development unfold in a group of very high risk adolescents with high policy significance. Information from this study will enrich theory about the differential and common effects of developmental change on substance use and crime and will provide guidance for assessing and intervening with adolescents the juvenile justice system.